The present invention relates to a piston and cylinder combination and more particularly to a piston-cylinder structural arrangement for high-pressure, hydraulic pumps or motors, including motor devices for control positioning of heavy loads, remote control positioning, remote control locating, servo positioning, and the like. Combination of dual piston-cylinder arrangements can provide push-pull or double-acting effects.
Specifically, the present invention is directed to the structural arrangement which provides for tight closure of the fluid, preferably hydraulic fluid within a working chamber, e.g. a cylindrical chamber of variable volume as defined by the position of a piston as one working member being disposed in a cylinder as the other working member. Such closure is effected by means of a deformable sealing member, preferably a flexible elastic sealing tube, preferably made of an elastomer which is attached at two locations having distance from each other, e.g. with its respective ends, to the working members, e.g. piston and cylinder, respectively to form a leakproof, sealed, tight connection for the closure of working fluid which may be under very high pressure, for example in the order of 100 at gauge.
Piston-cylinder arrangements for high pressure application provided with leakproof seals are difficult to use in continuous high-power applications in which high operating frequencies, high operating speeds and high pressure arise. The low mechanical strength of the sealing tubes has heretofore inhibited such applications because, to provide a leakproof, tight seal, the sealing tube must be secured to the working members which move relatively to each other so that the sealing member must undergo frequently repeated deformations under heavy forces pressing a surface of the member against a support surface in relation to which the member is partially moved. Therefore, high frictional forces arise which can be reduced only by special arrangements. Heat due to friction as well as the frictional force itself cause rapid deterioration of the elastic portions of the seal; typically of elastomer material. Moreover the sealing member generally has hereto been locally clamped and has been terminated by an abrupt transition on the respective support element, that is, the piston or the cylinder disposed at the end of the tube under consideration. These terminations resulted in high-stress gradients in radial direction at localized points or zones of the sealing tube. These high stresses greatly reduced the durability of the sealing tubes.